1. Field of the Invention
The invention relates to a moisture meter.
2. Prior Art Discussion
Our prior published British Patent Application No. GB2347220A describes a moisture meter which has a digital control circuit driving an LED output display. This meter has many advantageous features such as storage of readings and upload to a host computer, and choice of a range of different materials having different response characteristics.
In using a moisture meter for surveying a building it is desirable to hold the meter or probe against a wall or other surface and to move it across the surface. In this way the surveyor can see the trend in moisture readings as the meter moves from a dry to a wet part of a wall or other surface, and can survey the extent of the dampness and the size of the problem.
Use of a meter of the above type presents problems for surveyors as it is difficult to track trends on the display as the meter is moved. Very often the surveyor sees tumbling digits on the display, and not a clearly visible trend.
Another disadvantage of currently available moisture meters is that for some applications user interaction is complex.
A disadvantage of some analogue moisture meters is that in some applications the measuring locations are difficult to access and the operator may have to hold the meter out of sight while taking a measurement. The scale reading may change if the meter is then moved to a position where the scale can be read.
The invention is therefore directed towards providing a moisture meter to address these problems.
According to the invention, there is provided a moisture meter comprising:
a moisture sensor;
a digital control circuit comprising means for processing output signals from said sensor and for generating and storing moisture measurements; and
an output interface comprising a digital to analogue converter (DAC) connected to the digital control circuit, and an analogue display device comprising means for providing an analogue moisture display in response to outputs of the digital to analogue converter.
In one embodiment, the analogue display device comprises a moving coil meter.
In another embodiment, the moisture meter comprises means for linearising moisture readings.
In a further embodiment, the linearising means comprises a logarithmic amplifier in the sensor.
In one embodiment, the logarithmic amplifier is connected between a sensor amplifier and an analogue to digital converter (ADC) of the digital control circuit.
In another embodiment, the digital control circuit comprises an input interface comprising means for allowing user selection of a desired material.
In a further embodiment, the input interface comprises a user button for selecting a material.
In one embodiment, the digital control circuit comprises means for generating an interrupt upon user selection of a material.
In another embodiment, the digital control circuit comprises means for storing a flag indicating the selected material when the moisture meter is powered down, and for activating with the same material at power-up.
In a further embodiment, the digital control circuit comprises means for locking to a current reading in response to user selection of a hold function at the input interface.
In one embodiment, the digital control circuit comprises means for generating an interrupt upon user selection of the hold function.
In another embodiment, the digital control circuit comprises means for operating in timed loops of monitoring sensor signals, processing the signals, and outputting a moisture reading.
In a further embodiment, the digital control circuit comprises means for powering-down to a sleep mode after expiry of a timeout period for a single reading.
In one embodiment, the digital control circuit comprises means for activating a timer when a timed processing loop generates the same reading as that for the previous processing loop, whereby the timeout period is calculated from the time at which a reading has not changed.